Review of existing code

Welcome — in this lesson we’ll quickly review the existing application code to understand the project structure and the main Flask app behavior. This concise overview prepares you for containerizing and deploying the app to AWS. We use the AWS Cloud9 IDE in this walkthrough. If you work in CloudLabs, you’ll use Cloud9 or a similar development environment. In Cloud9 the repository aws-microservice-project is already available. Expanding the project shows several files and folders. The primary application logic lives in app.py.

The image shows a file directory in an AWS Cloud9 environment, highlighting a Python file named "app.py" within the "aws-microservice-project" folder.

Repository layout (high level)

File / Folder	Purpose	Notes / Example
`app.py`	Main Flask application	Primary focus for deployment and CI/CD work
`requirements.txt`	Python dependencies	Used to install packages in virtualenv or Docker image
`README`	Project documentation	Setup and run instructions
`templates/`	HTML templates	Rendered by Flask with `render_template()`
`static/`	Images, CSS, JS	Served as static assets by Flask

For the purposes of deployment and CI/CD, we will mainly modify and test app.py and requirements.txt. The templates and static folders are front-end assets typically managed by frontend engineers; we only need to run or serve them during testing.

What to expect in app.py Opening app.py reveals a concise Flask application. It may include a default username/password for local testing and implements a small set of routes that together provide a simple order flow:

A login (default) page
A product listing / welcome page
A place-order page for a selected product
A /submit_order endpoint that accepts form submissions

Example: the submit endpoint reads form fields from a POST request:

@app.route('/submit_order', methods=['POST'])
def submit_order():
    product_id = request.form['product_id']
    name = request.form['name']
    address = request.form['address']
    quantity = request.form['quantity']
    # process the order (business logic omitted here)
    return "Order received", 200

Using request.form['field'] raises a KeyError if the form field is missing. Prefer request.form.get('field') plus explicit validation to avoid runtime errors and improve security.

Route flow (user experience)

A user starts at the login page.
Successful login redirects to the product/welcome page (product listing).
Selecting a product opens the place-order page for that product.
Submitting the form posts to /submit_order, which processes the order and returns confirmation.

Tips for DevOps / local testing You do not need to understand every line of business logic to deploy the app, but you should be able to run and test it locally. Typical steps include:

Create and activate a Python virtual environment.
Install dependencies from requirements.txt (for local runs) or add them into a Docker image.
Run the Flask app in Cloud9 (or your IDE) to verify the UI and endpoints.
Containerize the app with Docker and test the container locally.
Verify endpoints (e.g., login, product list, place-order, /submit_order) behave as expected.

Suggested commands (examples)

Install dependencies:

python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt

Run locally (development server):

export FLASK_APP=app.py
flask run --host=0.0.0.0 --port=5000

Build and run Docker (example):

docker build -t aws-microservice-project .
docker run -p 5000:5000 aws-microservice-project

Course roadmap (what we’ll cover next)

Setting up Cloud9 and the development environment for Flask
Running and testing the app locally (end-to-end)
Dockerizing the application and preparing deployment artifacts for AWS
(Later) CI/CD pipelines and deploying the container to AWS services

Links and references

This review is your blueprint for preparing the app for deployment. Proceed to the next lesson where we run and validate the application locally.

Watch Video

Understanding the requirements from developers

Overview and setup Cloud9